Thank you for the details! I am aware of sitemaps limitations and I'm going to introduce a simple solution for that in the near future. Sitemaps could be automatically split into "chunks" (or like you said - sub-sitemaps). But right now there is no such a big blog on Engrave for which it could be a problem :)

I believe that using Google Search Console is much better than submitting sitemaps automatically because of useful information (like search positions, CTRs, etc) this service provides. I will, of course, consider pushing those sitemaps automatically to the services mentioned by you but for now - let bloggers do that manually :)